Targeting is the key.
The key in marketing is to identify your target customers and then focus your attention (i.e. money) on reaching and influencing those customers.We can all guess who our target audience is, and we may be pretty close, but there are always going to be people out there that we didn’t expect to be potential customers. That’s one of the great things about using keywords and Google’s immense data set of people using those words for searching the web.
If someone searches for our product/service, Google will know about it, even if they are not one of the people we would normally target. By the same token, we may spend money on fruitless leads because they were searching for something similar sounding to what we offer, and we didn’t do enough work to differentiate that.
It’s a continual process to take a guess at what words/phrases to use and how productive they actually are.